PW20 New Approaches to Determining Soil and Sediment Exposures
Exhibit Hall
8:00 AM - Wednesday
(PW287) A simple scheme to determine the potential chemical toxicity of mine wastes.
Wildeman, T 1, Ranville, J1, Smith, K2, 1 Colorado School of Mines, Golden, CO, USA2 U.S. Geological Survey, Lakewood, CO, USA
ABSTRACT- A decision tree that uses simple physical and chemical tests has been developed to determine whether a mine waste poses a toxicity threat to the aquatic environment. For the chemical portion of the tree, three leach tests have been extensively used: 1) one recently developed by the U.S. Geological Survey (USGS); 2) a test used by the Colorado Division of Minerals and Geology (CDMG); and 3) a modified version of the 1311 TCLP (Toxicity Characteristic Leaching Procedure) EPA test. The multi-element power of modern inductively coupled plasma, atomic-emission spectroscopy (ICP-AES) is also a necessary component of the scheme. At two sites in Colorado, one in Virginia Canyon in the Idaho Springs/Central City Superfund Site and one in the Upper Animas River Basin, 25 streambed-sediment samples and water flowing over them were collected. General field parameters (e.g., pH, specific conductance, temperature) were measured. Stream-water samples and leachates from the three leach tests performed on the streambed sediments were analyzed for 31 elements by ICP-AES. Element concentration pattern graphs (ECPG) were generated that compare selected groups of elements from the three leach tests with the same elements in the stream water. When the pH values of a water sample and its corresponding leachates were below 5, the element-concentration patterns of all four solutions were similar and aquatic toxicity from metals, such as Pb, Cu, Zn, Mn and Al, was clearly indicated. When the pH values of a water sample and its corresponding leachates were above 5, the element concentration patterns from the four solutions were different and inferred aquatic toxicity depended on the leach test. It appears that in stream water with a pH of less than 5, the metals that strongly affect aquatic toxicity are soluble, organic complexes are minimal, and there is negligible carbonate alkalinity. All these factors tend to make the water toxic to most organisms.
Key words: metal contaminants, aquatic toxicity, aquatic chemistry